The present invention relates to a process for producing a fresh wiping solution and for treating this wiping solution contaminated by the inks from one or more intaglio printing machines operating in a closed circuit and to an apparatus for carrying out this process.
In intaglio printing machines, the printing plates mounted on the plate cylinder, into which the designs are engraved, are wiped by rubbing with a wiping cylinder which rotates in the same direction as the plate cylinder and which removes the ink found outside the intaglio cuts of the plate. In order to clean the ink found on the wiping cylinder, the lower part of the latter is situated in a wiping tank, this tank being equipped, in addition, with brushes and doctor blades. A system of nozzles squirts fresh wiping solution onto the wiping cylinder and the fresh solution, once mixed with the ink, exits from the wiping tank as used solution.
By way of example, U.S. Pat. No. 5,390,598 discloses such a plant for the continuous cleaning of the wiping cylinder in an intaglio printing machine.
Novel inks have now been developed and the latter make it possible to employ a wiping process using a water-based solution which is much less environmentally harmful than the wiping solutions used previously. These novel inks used in the intaglio printing process are known, for example, from U.S. Pat. No. 4,966,628 and EP 0 340 163. Such inks comprise, inter alia, oleoresinous components and pigments. Water-based wiping solutions used in such intaglio printing machines with these novel inks are also known in the state of the art and these wiping solutions generally comprise at least 90% of water and additives.
One of these wiping solutions is disclosed in Patent DE 1 546 776 and is composed of an aqueous solution comprising 1 to 5% by weight of alkaline lye, 2 to 10% by weight of a commercial cleaning product comprising alkaline phosphate and 1 to 10% by weight of a wetting agent. More particularly, this aqueous solution comprises 1.5 to 2.5% by weight of caustic soda NaOH, 2 to 5% by weight of sodium phosphate Na3PO4 and 1 to 3% by weight of sulfonated castor oil.
Another of these wiping solutions is disclosed in U.S. Pat. No. 3,389,656 and is composed of an aqueous solution comprising approximately 1 to 5% by weight of a strong base, such as, for example, potassium hydroxide or sodium hydroxide or alternatively ammonium hydroxide, approximately 2 to 10% by weight of a detergent, for example sodium polyphosphate, and approximately 0.3 to 10% by weight of a wetting agent, such as sulfonated castor oil.
Novel inks which have appeared on the market recently have even rendered unnecessary the additives added to water in the wiping solutions described above. Thus, the wiping solution can even be composed solely of softened water.
A process for producing fresh wiping solution and for treating used wiping solution known in the prior art comprises the following steps:
a) production of fresh wiping solution,
b) introduction of the fresh wiping solution into one or more wiping tanks and contamination by the inks,
c) ultrafiltration of the used solution coming from the wiping tank or tanks, producing a clear solution and a concentrated residual solution,
d) recycling the clear solution into the fresh wiping solution circuit,
e) flocculation of the concentrated residual solution resulting from the ultrafiltration,
f) filtration of the flocculated solution, giving solid residues and a solution,
g) neutralization of the filtered solution with acid,
h) reduction of the chemical oxygen demand of the neutralized solution, and
i) discharge to drain of the solution with the reduced chemical oxygen demand.
An example of such a process is given in block diagram form in FIG. 1.
The recycling capacity of this process after ultrafiltration is approximately 80%, this value depending in addition on the quality of the ink used and on its concentration in the wiping solution.
The major disadvantage of this process is that the treated residual solution conveyed to drain comprises a large amount of salts. These salts are mainly chlorides, originating from the flocculation and neutralization products, and sulfates, if sulfuric acid has been used for the neutralization. The presence of a large amount of chlorides and/or of sulfates, as well as the chemical oxygen demand, which can be greatly reduced but not entirely eliminated, presents problems in many countries.
In addition, depending on the number of machines used, the consumption of water and of flocculation products can be high and expensive.
The aim of the invention is to improve the known processes for the recycling of wiping solution.
The aim of the present invention is more particularly to produce a process, operating in a closed circuit, in which most of the wiping solution is recovered and no longer discharged to drain in the form of water after an appropriate treatment. The water consumption of the process can thus be greatly decreased and only solid waste will be obtained, which waste can subsequently be treated while observing environmental protection standards.
The invention also makes it possible to no longer use active charcoal, which corrected the chemical oxygen demand.
The present invention constitutes an improvement to the process and the apparatus which form the subject-matter of Swiss Patent Application No. 1996 2152/96, filed on behalf of the same Applicant, which has not yet been published.
The process for producing fresh wiping solution and for treating used wiping solution according to the invention is defined by the steps of claim 1. This process makes it possible to treat both wiping solutions composed solely of softened water and wiping solutions composed of softened water and of additives.
In particular, the process according to the invention for the treatment of used solution involves a chemical agent which separates the inks from the wiping solution in step (c). This chemical agent exhibits the advantage, on the one hand, of not modifying the physicochemical properties of the wiping solution and, on the other hand, of not increasing the volume of the solid residues. The chemical agent is formed by an organic copolymer which has the following properties:
relative density, 1.08-1.09 kg/dm3 
pH, approximately 7
molecular weight, approximately 500,000
Brookfield viscosity, 10,000 cPs.
The action of this chemical agent is similar to that of a conventional flocculant but, on the other hand, the wiping solution can be reused immediately after ultrafiltration, since its properties are not modified.
The chemical agent can optionally be mixed with an inorganic product which reacts on the potential of the ink molecules present in the solution, by destabilizing them.
The dependent claims 2 to 5 define specific embodiments of the process according to the invention.
The independent claim 6 defines an apparatus for the implementation of the process according to the invention.
The dependent claims 7 to 10 define specific embodiments of the apparatus for the implementation of the process.